1. Field of the Invention
The invention relates to a vehicle including an engine and a battery and a control method for the vehicle.
2. Description of Related Art
In a vehicle including an engine and a battery (a so-called hybrid vehicle), as described in Japanese Patent Application Publication No. 2000-092614 (JP 2000-092614 A) and the like, the power of the engine is transmitted to a generator to cause the generator to generate electric power and the battery is charged using the electric power generated by the generator. As described in Japanese Patent Application Publication No. 2009-286174 (JP 2009-286174 A) and the like, as the operation of the engine, there are a load operation and a self-supported operation.
In the load operation, the power of the engine is transmitted to the generator and the power generation by the generator is performed. The load operation is performed, for example, when a state of charge (SOC) of the battery decreases and the battery needs to be charged. In the self-supported operation, the engine is operating but the power generation by the generator is not performed. The self-supported operation is performed, for example, when the engine is used as a heat source in order to heat the interior of the vehicle.
The operation of the engine is switched between the load operation and the self-supported operation according to command power to the engine. Specifically, when the command power to the engine is larger than command power set in advance (a threshold), the load operation is performed. When the command power to the engine is smaller than the command power set in advance (the threshold), the self-supported operation is performed.
When the command power to the engine is near the command power set in advance (the threshold) and changes according to pulsation or the like of the engine, the command power to the engine sometimes changes between a value larger than the threshold and a value smaller than the threshold. Consequently, the operation of the engine is switched between the load operation and the self-supported operation. In particular, when the fluctuations in the command power to the engine are repeated in a range including the threshold, the operation of the engine is frequently switched between the load operation and the self-supported operation.
If the electric power can be supplied from the generator to the battery, it is possible to increase the command power to the engine and continue the load operation. However, when the charging of the battery is limited and it is hard to supply the electric power from the generator to the battery, the command power to the engine less easily increases. Consequently, the command power to the engine tends to stay near the threshold. As explained above, the operation of the engine is sometimes frequently switched between the load operation and the self-supported operation.
In the load operation and the self-supported operation, engine speeds are different from each other. Therefore, when the operation of the engine is frequently switched between the load operation and the self-supported operation, engine speed sometimes frequently changes to give a sense of discomfort to a user.